The overall objective of this research is to define the role of estrogen-induced uterine-, kidney-\and pituitary tumor-derived growth factors in the proliferation of rat pituitary tumor cells in vivo and in vitro. The rat pituitary tumor lines to be used in these studies are the GH3/C14 and GH[unreadable]9[unreadable]C[unreadable]1[unreadable] cells. Our studies with these lines have shown that estrogens are required for optimal growth in vivo but are not capable of promoting continuous growth of these cells in vitro. We have considered several possible explanations for these observations in culture; however, our most recent approach has been to ask whether the mitogenic role of estrogens in vivo may be mediated by steroid hormone control of the production and secretion of growth factors specific for the hormone-responsive pituitary tumor cells. To evaluate the possibility of a mediated mechanism involving estrogen-induced polypeptide growth factor, we first prepared extracts of tissues removed from estrogen-treated and estrogen-deficient animals and assayed for growth activity by addition of extracts to cells in serum-free medium. Our experiments demonstrate that estrogens elevate the levels of growth factors for GH3/ C15 pituitary cells in extracts of both rat uterine and rat kidney tissue. We have now purified pituitary tumor cell growth factors from lyophilized powders of sheep uteri and kidneys. These activities are related, but not identical, polypeptides of Mr = 4,200. These properties are now under further investigation. In addition, autocrine/parocrine growth factor (Mr 70,000) have been identified in pituitary tumors. To date, our experiments suggest a model of hormone-responsive pituitary tumor growth in vivo that includes a mechanism that involves uterus, kidney, and an autocrime mechanism of tumors producing specific polypeptide growth factors locally within estrogenresponsive and autonomous tumors. (D)